1. A conventional telephone line with 3 kHz bandwidth and having 30 dB signal-to-noise ratios can carry information at a rate of

- 15 kbps
- 30 kbps
- 16 Mbps
- 3 kbps

2. If the probability of a message is 1/4, then the information in bits is

- 1 bit
- 2 bit
- 4 bit
- 8 bit

3. Digital modulation techniques are used in a satellite communication system, because

- they are easier to handle
- large bandwidth utilization is possible
- they have a spectral efficiency
- they are less prone to interference

4. A TDM link has 20 signal channels and each channel is sampled at 8 kHz. Each sample is represented by 7 bits and contains an additional bit for synchronization. The total bit rate for the TDM link is

- 1180 kbps
- 1128 kbps
- 128 Mbps
- 1280 kbps

5. Frequency frogging is used in the carrier system to

- Conserve frequencies
- Reduce distortion
- Reduce cross talk
- Reduce bandwidth

6. Digital modulating system among the following is

- PCM
- PPM
- PFM
- PWM

7. A binary data is to be sent at the rate of 100 kbps over a channel with 60 dB transmission loss and noise power spectral density N_{o} = 10^{-12} W/Hz at the receiver. The digital modulation system that will require minimal transmitted power if the probability of error is to be maintained at 10^{-3} is

- Non-coherent ASK
- Coherent BFSK
- 16-array PSK
- BPSK

8. MSK (Minimum Shift Keying) is an orthogonal FSK scheme that gets its name from the fact that

- the phase shift is minimum.
- the error probability is minimum.
- the transmission power required is minimum.
- the transmission bandwidth required is minimum.

9. Which one of the following statements is incorrect about the matched filter?

- The maximum output SNR depends on the input signal energy
- The impulse response is reversed delayed version of the input signal
- The error probability depends on the wave shape of the signal
- Matched filter and correlator gives identical reception performances.

10. A digital communication system uses 8-PSK modulation and transmits 3600 bps. What is the symbol rate?

- 10800 symbols/sec
- 450 symbols/sec
- 28800 symbols/sec
- 1200 symbols/sec

11. Which signalling scheme is most affected by noise?

- ASK
- FSK
- PSK
- QAM

12. In the case of data transmission, which one of the following systems will give the maximum probability of error?

- ASK
- FSK
- PSK
- DPSK

13. Which one of the following statements is correct?

For coherent detection of digital signals, the receiver must be

- synchronized in time only
- synchronized in phase only
- unsynchronized in time and phase
- unsynchronized

14. A modulation technique in which bandwidth of the modulated signal is extended well beyond the bandwidth of the modulating signal, independent of the modulating signal bandwidth, is called

- Wide-band modulation
- Extended bandwidth modulation
- Spread spectrum modulation
- Narrow-band modulation